Edge testing medium



July 23, 1935. R- w, BROWN 2,008,679

EDGE TESTING MEDIUM Filed Oct. 19, 1952 Patented July 23, 1935 h A I 1 2,008,679

1 UNITED stares mm ori ice EDGE TESTING-MEDIUM Roberto Brown, Boston, Mass. w Applicationoctober 19, 1932, Serial No. 638,544

8 Claims. (01. 73-51 Theuobject of the present inventionis to provide a satisfactory medium for testing" the keenness of cutting edges, for instance and particularly the. edges of razor blades. In a prior application for patentfierial No. 570,672, filed October 23, 1931, I havedisclos'ed an apparatus for testing the keenness of safety razor blades and the like, in which the: testing medium comp-rises one crmore strings orthreads against which the 10 bladebeing testedis pressed with a regulated degree of force, so that the depth of incision made bythe blade, or the absence of cutting effect under the controlled pressure, is ameasure of the keenness of theedge. I a In the search for a commercially suitable medium, in which low cost is an'importantconsid- 'eration, I have used heavy threadJmade of raw cotton, suchas can .be obtained from many sources. in the open market; "Experience with this material has shown that, while it isentirely satisfactory for all of themakes of wafer blades in use up to a recent date, it'does not serve satis- 'factorily with certain blades which have lately appeared on the market. Such blades are of extreme hardness, and it appears that when tested in the manner above described. with strands of raw cotton, their edges are injured. The injury coi ists, in a perceptible. diminution of keenness. As the, result of many observations and careful study I have concluded that theprobable cause of such injury is the harshness of the cellulose which constitutes; cotton fibers and the brittleness of thesteel particles at the fine edge of'theseextr'emely hard blades. The problem which I have solved by the presentinvention has been to devise a medium which is less harsh than raw cotton fibers, so that it may be penetrated. by a sharp edge of brittle steel alloy: without injury to the edge, while at the same time having sufficient resistance to penetration to aiiord discrimination between different degrees of sharpness of different edges. This constitutes the main object and accomplishment of the invention Another object has been to devise a testing element of such close. approximation to circular outline in cross section, coupled with such firmness of structure, that it will interposc a substantially equal thickness between the blade edge and the abutment against which it is pressed by the blade in the course of a test, no matterwhich side, or part of its circumfer ence, faces toward the blade. The means by which I have accomplished these objects constitute the essence of the invention, which can best be explained in connection with a detailed de scription of one embodiment thereof. Such'de:

scription is given in connection with ,an illus trative drawing, in which I Fig. 1 is a plan view of an apparatus for treating the raw material of which my new testing of 1 such treating apparatus;

Fig. 3 is a perspective view and section of a partially dismembered fragment of the testing medium.

' The particular testing medium here illustrated is constructed of cotton fiber built up of a plurality of strands so disposed as to give the desired superficial contour and firmness of structure. These strands comprise straight core strands a, w and enveloping helical surface strands b, b. There may be any number of the core strands from one upward, but I consider that seven is thebest number, inasmuch as seven strands of approximately equal diameter automatically assume a hexagonal arrangement when bunched together and put under tension, and make a com pact core of which the circumference in cross section is a somewhat near approximation to a circle. The surface strands are more numerous and are twisted helicallyaround the core with such a pitch or lead that they lie smoothly side by side in contact with one another. t is immaterial whether the outer strands are larger or smaller than the core strands. I find it desirable to'provide, them in such diameter and number that when twisted about the core with a helix angle of approximately 30, they will lie in close contact with one another and the straight line tangent to the outside of any two adjacent strands will closely approximate the position of the circular arc tangent to the same two strands and concentric with the core. This in order that the blade edge to be tested will engage the composite structure at approximatel the same distance from the center of the latter whether it happens to come tangent to two strands simultaneously or to one strand only. It will be understood by reference to my prior application that the testing medium is fed lengthwise a short distance, perpendicularly to the plane in which the blades are held while being tested, after each test, wherefore the angular relationship of the outer strands to the successive blades is constantly changed, due to the helical arrangement of the strands. 3 v I The diameter of the testing medium is such that it interposes a sufiicient mass and thickness of matterbetween the blade edge and the backing abutment to permit a measurablediiference of movement of the blade under controlled press re, according to whether it easilycuts the medium, or cuts it with diiiiculty or not at all. At the same time the mass and thickness should not be so great as to'reduire a sharp blade to cut through an unnecessary mass of fibers, Without intending to limit myself to exact dimensions, I may say that I have found that a testing medium, when made as above described with strands which give it a total diameter of from twenty-five thousandths to forty-five thousandths of an inch is satisfactory.

The testing medium, whether of the above described construction, or any other construction suitable for the purpose, is subjected to a heat treatment sufficient to make the fibers less tough, and therefore more easily severable by a fine edge. I have made many tests and experiments to determine the best degree and extent of this heat treatment. I have found that with strands made from Egyptian cotton a temperature of 485 F. with subjection of the material to this temperature for twenty minutes seems to give the best results. A somewhat higher temperature, approximately 492 F. seems to give the best results with American cotton. Considerable variation from these temperatures and time periods is permissible. For instance, bleached cotton does not require so high a temperature as unbleached cotton, other things being equal; and longer treatment at lower temperatures, or shorter treatment at higher temperatures may give substantially as good results. A rough test of suflioienoy is the change of color to a shade approaching dark brown.

lfhis heat treatment efiects a change in the material which may be in the nature of a partial distillation. It reduces both thehardness and tensile strength of the strands, but leaves sufficient firmness and resistance to effect the de sired discrimination between sharp, dull and medium sharp edges.

Figs. 1 and 2 show a suitable apparatus for carrying out the heat treatment. A tank 1 containing a body of liquid 2 is heated by suitable means, such as a gas burner 3. The liquid may be oil, such as lard oil, or any other liquid which is capable of being elevated to such a temperature as those previously indicated and will remain fiuid at the ordinary temperatures.

An inner container 4, wherein a mass or skein 5 of the fibrous testing element is placed, has a etachable tight cover 5 and is'rotatably supported by alined bearings l and 8. The latter bearing is carried by a bridge 9 detachably mounted across the open upper end of tank I. A vent tube l9 passes through the cover 6 and serves also as a spindle for locating and rotating the container 6. A gear I l fastened to such spindle meshes with a driving gear 12 which is driven by a hand crank l3 and supported by a bearing 94 on the bridge 9. A thermometer I5 is suspended into the liquid bath from a bracket IS on the bridge.

Rotation of the container 4 serves to agitate the liquid and distribute the heating effect uniformly throughout its whole substance. Such agitation is facilitated by vanes I! on the outside of the container. Moisture and gases liberated from the fibrous material by heat escape through the bore of tube I0.

Although I have herein described the structure and process of treating my improved testing medium as applied to a structure made of cotton fiber, I wish to make it understood that I do not limit my protection to structures made of cotton only, but claim all benefits of novelty and utility in the application of the invention to all other fibrous structures to which it may be usefully applied.

What I claim and desire to secure by Letters Patent is:

I. A testing medium for determining the relative keenness of cutting edges, consisting of nonmineral fibers assembled in a compact mass, the natural harshness of which has been modified by heat treatment to the condition in which it can be incised by a sharp blade under a given pressure and incised to a less distance or not at all by a relatively dull blade under the same pressure.

2. A testing medium for determining the relative keenness of cutting edges, consisting of nonmineral fibers assembled in a compact strand, the natural harshness of which has been modified by heat treatment to the condition in which it can be incised by a sharp blade under a given pressure and incised to a less distance or not at all by a relatively dull blade under the same pressure, while havingsufficient tensile strength to be displaceable by endwise pull after partial severance by such sharp blade.

3. A testing medium for determining the relative keenness of cutting edges, consisting of a compact mass of non-mineral fibers having qualities of incisability and resistance to incision such that it will be incised by an extremely sharp wafer type blade of substantially glass-hard steel composition under a pressure of given force exerted in a direction substantially in the plane of the blade and perpendicular to the cutting edge thereof, without injury to such edge, but will not be severed by dull blades under the same pressure similarly exerted.

4. A testing medium for determining the relative keenness of cutting edges, consisting of cotton fibers inter-engaged in the form of a cord and having qualities of incisability by keenest edges, resistance to incision by relatively dull edges, and lack of harshness such as are imparted by heat treatment of such fibers at a temperature between 440 F. and 510 F. for a period between ten and thirty minutes.

5. A testing medium for determining the relative keenness of cutting edges, consisting of cotton fibers inter-engaged in the form of a cord and having qualities of incisability by keenest edges, resistance to incision by relatively dull edges, and lack of harshness such as are im parted by heat treatment of such fibers at a temperature of approximately 485 F. for a period of approximately twenty minutes.

6. A testing mediumfor determining the relative keenness of cutting edges, consisting of American cotton fibers interengaged in the form of a cord and having qualities of incisability by keenest edges, resistance to incision by relatively dull edges, and lack of harshness such as are imparted by heat treatment of such fibers at a temperature of approximately 492 F. for a period of approximately twenty minutes.

7. An edge testing medium consisting of a cord of cotton fibers converted by semi-distillation under heat to a condition in which the fibers have less than their original hardness and toughness, to such extent as to be incisable by the edge of the keenest glass-hard razor blades under direct pressure of given amount in the plane of the blade without sensible injury to the keenness of such edge, while retaining sufiicient cohesion to give a measurably greater resistance to a relatively dull blade under the same pressure.

8. A testing medium comprising a composite structure consisting of fibrous core strands and helical superficial strands surrounding the core; the whole assemblage being composed of-semidistilled fiber.

ROBERTO W. BROWN, 

